Thomas Kenan and Elizabeth Johnstone

Almost evey reference I find indicates Thomas Kenan's wife was the daughter of Capt. John Johnstone and Elizabeth Belchier.This would make her the sister of Governor Gabriel Johnston.Yet, Gabriel's sister was alive at his death in 1753, and is listed in his will as Elizabeth Smear (Sister: Elizabeth Smear, of the County of Fife in North Britain - "To my sister Elizabeth Smear my large gold watch.")

One reference refers to her as his niece...if so, which of John Johnstone's children would be her father?